The present invention relates to measuring apparatus and method for thickness fluctuation in a thin board, and more particularly relates to measuring apparatus and method for a thin board for measuring and evaluating thickness fluctuation in the thin board which is required to have less thickness fluctuation in the plane direction that is orthogonal to the thickness direction thereof such as wafers for semiconductor manufacturing.
A conventional measuring apparatus for a thin board is described with reference to FIG. 19 to FIG. 23.
FIG. 19 is a schematic configuration view showing a first example of the conventional measuring apparatus for a thin board.
In FIG. 19, a thin board W is retained by retaining members 2a, 2b, 2c on a rotor 1 which is positioned inside the inner radius of a hollow spindle. The rotor 1 is rotated in the state in which the thin board W is retained, while a sensor unit 3 which moves in a linear direction is moved in conjunction with the rotation of the rotor 1, by which the thickness of the thin board W is measured in a spiral fashion (see, e.g., U.S. Pat. No. 4,280,354).
FIG. 20 and FIG. 21 are schematic configuration views showing a second example of the conventional measuring apparatus for a thin board, in which a thin board W is retained by a rotating rotor 4. FIG. 21 is a detailed view showing a measuring section in the second example of the measuring apparatus.
In FIG. 21, a stator 5 is provided on the outer circumference of the rotor 4, and the rotor 4 is supported by a pressure source inside the stator 5. The thin board W is retained by retaining members 6a, 6b, 6c provided on the rotating rotor 4. Therefore, the thin board W is disposed in the vicinity of the rotating rotor 4. In the state where the thin board W is retained, the rotor 4 is rotated while a sensor unit 7, which moves in linear direction, is moved in conjunction with the rotation of the rotor 4, by which the thickness of the thin board W is measured in a spiral fashion (see, e.g., Japanese unexamined patent publication No. 10-70162).
FIG. 22 is a schematic configuration view showing a third example of the conventional measuring apparatus for a thin board.
In FIG. 22, a thin board W is retained in a hollow spindle 8, and an optical probe composed of a stage 9 and an optical displacement gauge 10 for measuring displacement magnitude of interference fringes is moved in conjunction with the rotation of a rotor which is composed of the hollow spindle 8 and retains the thin board W, by which a plane of the thin board W is scanned through a spiral route and measurement of the thin board W is performed. In this case, scan and measurement are extended to an outer circumferential portion of the thin board W where there is a notch indicating crystal orientation of a wafer that is the thin board W (see, e.g., Japanese unexamined patent publication No. 2000-283728).
In the above-described conventional apparatus and measuring methods, the rotor 4 is disposed inside the stator 5 as shown in FIG. 23. According to this configuration, it becomes possible to make the shape of the rotor 4 more compact to facilitate manufacture of the apparatus, as well as to decrease a moment of inertia of the rotor 4 to facilitate acceleration/deceleration of the rotor 4. However, the configuration in which the rotor 4 is disposed inside the stator 5 causes the following problems. That is, since the thin board w is retained by the retaining members 6 in the center portion of the ring-shaped rotor 4, and the rotor 4 is present in the vicinity of the thin board w, rotation of the rotor 4 around a central axis 4a in the axial direction generates wind 4c in a hollow section 4b of the rotor 4. The wind 4c vibrates the thin board w and deteriorates measurement precision of the thin board w. Further, there is also a problem in that the widely exposed rotor portion which rotates presents a danger. Moreover, since the rotor is provided inside the stator, a large aperture hole on the stator for mounting of the rotor degrades the rigidity of the stator. Consequently, the rotation of the rotor generates vibration of the apparatus and further deteriorates measurement precision of the thin board w, while at the same time the rotation of the rotor distorted in a thrust direction further deteriorates measurement precision of the thin board w. Moreover, since the rotor is provided inside the stator, heat generated in a rotor driving section may tend to be trapped inside, thereby causing the measuring apparatus itself to be subject to thermal expansion and thereby affect the measurement precision of the thin board w.